Association Between Serum Sodium and Long-Term Mortality in Critically Ill Patients with Comorbid Chronic Obstructive Pulmonary Disease: Analysis from the MIMIC-IV Database

Abstract

Purpose: The purpose of our study was to investigate the relationship between serum sodium levels and 1-year and 3-year mortality in critically ill patients with comorbid chronic obstructive pulmonary disease using real-world data.

Methods: The data of this study were collected from the Medical Information Mart for Intensive Care-IV (MIMIC-IV) database. First of all, we used the Kaplan-Meier curves and multivariable Cox regression analyses to measure the relationship between serum sodium levels and 1-year and 3-year mortality for critically ill patients with comorbid COPD. Next, a restricted cubic spline was used to analyze non-parametrically the relationship between mortality and serum sodium as a continuous variable. In addition, we also analyzed the mortality of different subgroups.

Results: A total of 5540 eligible subjects were extracted. Compared to normal serum sodium levels, adjusted multivariable Cox regression analysis confirmed that hyponatremia and hypernatremia were still significantly associated with 1-year mortality (HR = 1.551, 95% CI = 1.333~1.805, P<0.001; HR = 1.683, 95% CI = 1.317~2.151, P<0.001, respectively) and 3-year mortality (HR = 1.507, 95% CI = 1.302~1.744, P<0.001; HR = 1.612, 95% CI = 1.269~2.048, P<0.001, respectively). In patients with or without adjustment variables, there was an obvious U-shaped non-linear relationship between serum sodium levels and 1-year and 3-year mortality with a reference level of 139 mmol/L, which indicated that patients in both hyponatremia and hypernatremia had higher mortality than normal serum sodium levels.

Conclusion: This study showed that both hyponatremia and hypernatremia were related to increased 1-year and 3-year mortality in critically ill patients with comorbid COPD, which provides a new reference for the control strategy of correcting serum sodium levels.

Keywords: MIMIC-IV; chronic obstructive pulmonary disease; intensive care unit; serum sodium.

Figure 1

Flow chart of cohort selection.

Figure 2

Kaplan–Meier survival curves showing the association between serum sodium and all-cause mortality: (A) 1-year mortality; (B) 3-year mortality. Participants were divided into 3 groups based on serum sodium levels: the red line represents hyponatremia group (<135mmol/L), the blue line represents control group (135–145mmol/L), the black line represents hypernatremia group (>145mmol/L).

Figure 3

Association between serum sodium and clinical outcomes for patients with COPD in different multivariable models. (A, C and E) association between serum sodium and 1-year mortality for patients with COPD. (B, D and F) association between serum sodium and 3-year mortality for patients with COPD. Adjusted I for age, gender, race and insurance status; Adjusted II for age, gender, race and insurance status, SOFA score, glucocorticoid use, vasopressin use, invasive mechanical ventilation use, bacterial pneumonia, ventilator-associated pneumonia, hypertension, myocardial infarction, congestive heart failure, renal disease, liver disease and malignant cancer.